1. Field of the Invention
This invention relates to a semiconductor device provided with a fuse for a redundancy circuit as seen in a embedded memory device, and in particular, to a semiconductor device which is improved in the fuse and pad portions thereof, and to a method for manufacturing such a semiconductor device.
2. Description of the Related Art
When a fuse for utilizing a redundancy technique is formed on a surface of semiconductor substrate, the fuse is conventionally formed in a metal wiring layer which is disposed next to the second layer as counted downward from the metal pad. However, concomitant with the recent trend to further multiply the wiring layers, the metal wiring layer which is disposed below next to the uppermost metal wiring layer is prone to be made larger in thickness, resulting in an increase in thickness also of the interlayer insulating film which is disposed on the surface of the fuse.
On the occasion of forming a fuse window, it is required not only to work this thickened interlayer insulating film but also to leave the interlayer insulating film on the surface of the fuse. In spite of the requirement that the film thickness of the interlayer insulating film to be left behind on the surface of the fuse be made as thin as possible in order to enable the fuse to be stably cut out by laser blow, the interlayer insulating film to be worked is made very large in thickness, as explained above, thereby making it very difficult to control the working of the interlayer insulating film.
Further, in order to comply with the enhancement of the processing speed of semiconductor devices in recent years, the minimization of the delay of electric current in the metal wiring has become an major problem. It has been considered necessary to employ, as a countermeasure for solving the aforementioned problem, an insulating film which is low in dielectric constant (low-k film) as an interlayer insulating film to be interposed between the metal wirings. In this case, it is quite conceivable to fabricate a structure where this low-k film is disposed next to the second layer as counted downward from the metal pad. If so, the fuse in this low-k film will be cut out by laser blow, which however leads to the damage of this low-k film by the laser blow, thus badly affecting the characteristics and reliability of the semiconductor device.
As explained above, in the case of a semiconductor device such as a embedded memory device, concomitant with the trend to multiply wiring layers, the metal wiring layer which is disposed below next to the uppermost metal wiring layer as well as the interlayer insulating film disposed on the surface of the fuse are prone to be made larger in thickness, and due to this increase in thickness of the interlayer insulating film, it has become very difficult to control the working of the interlayer insulating film on the occasion of forming a fuse window. Further, when a low-k film is employed as an interlayer insulating film in order to enhance the processing speed of semiconductor device, this low-k film will be damaged by the laser blow to be employed in the cutting of the fuse, thus badly affecting the characteristics and reliability of the semiconductor device.